A Lut-Based Method to Estimate Clear-Sky Instantaneous Land Surface Shortwave Downward Radiation and its Direct Component from Modis Data

Land surface shortwave downward radiation (SWDR) is generally defined as incident solar energy over land surfaces in the shortwave spectrum (300-3000nm). As one of important parameter of the land surface radiation budget (SRB) and many land process models, it is usually required as part of the input variables to address a large variety of scientific application issues in fields of agricultural management, climate trends, ecological forecasting, reusable energy production, public health and so on. Currently, regional or global SWDR can be estimated from polar-orbiting or geostationary satellite observations based on empirical or physical-based retrieval models. These remote-sensed SWDR products with fine spatial resolution provide us valuable information about a series of critical Earth science problems and enable us to gain more insight into the planet we live on. In this paper, an improved method was proposed based on a look-up table approach via MODTRAN-5 simulations to estimate clear-sky instantaneous SWDR and its direct component from TOA radiance of Moderate Resolution Imaging Spectrometer (MODIS) observation. Ground measurements from seven SURFRAD sites are used for validating the algorithm and the result shows good accuracy. This approach is suitable for producing clear-sky instantaneous SWDR and its direct component at the spatial resolution of finer than 5 km.